There are 7 pollutants that are of concern in the 'Air Quality Strategy for England, Scotland, Wales and Northern Ireland' because of their potential health effects.
Benzene
Sources: Volatile Organic Compounds are released in vehicle exhaust gases either as unburned fuels or as combustion products, and are also emitted by the evaporation of solvents and motor fuels. Benzene is a Volatile Organic Compound which is a minor constituent of petrol.
The main sources of benzene in the atmosphere in Europe are the distribution and combustion of petrol. Of these, combustion by petrol vehicles is the single biggest source (70% of total emissions).
Effects: Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
1,3-butadiene
Sources: This is another organic chemical associated with traffic. It is not present in vehicle fuel, but is formed by chemical reactions when fuels are burnt and is emitted in the exhaust.
It is also used industrially, mainly in the production of synthetic rubber for tyres. At the few locations where it is handled in bulk, industrial sources may be significant, but generally traffic is the only significant source.
Effects: Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.
Carbon Monoxide
Sources: Carbon monoxide (CO) is a toxic gas which is emitted into the atmosphere as a result of combustion processes, and is also formed by the oxidation of hydrocarbons and other organic compounds.
In European urban areas, CO is produced almost entirely (90%) from road traffic emissions. It survives in the atmosphere for a period of approximately one month but is eventually oxidised to carbon dioxide (CO2).
Effects: This gas prevents the normal transport of oxygen by the blood. This can lead to a significant reduction in the supply of oxygen to the heart, particularly in people suffering from heart disease.
Lead
Sources: Lead is widely used in manufacturing articles and products. The largest use is in batteries, but it is used as an alloy (solders, gunmetal), in pigments, as well as in its pure state as a metal. It has also been used as a compound, tetraethyl lead, in petrol to improve its performance.
With leaded petrol having been removed from the market, and the almost standard use of catalytic converters on modern cars, output from road traffic is minimal. The primary source is now the metals industry.
Effects: Lead in air may affect people either by being absorbed through the lungs or through the digestive tract when it settles out, contaminating soil, dusts, water, and hence food. Lead, taken into the body, causes bio-toxic effects in a range of body systems.
At the low levels to which the public are exposed, the effects of concern are on the growth of blood cells, on the nervous system, and on blood pressure. Because of the fact that they are growing, children are likely to be more susceptible than adults are.
And there is concern that chronic exposure to levels of lead lower than those necessary to produce symptoms of lead poisoning can have subtle effects on neurophysiological function, and perhaps may prevent children achieving their full mental and physical potential.
Nitrogen dioxide
Sources: Nitrogen Dioxide is an acid gas produced by any combustion in air. The largest source is road transport, followed by the power generation industry, industry and commerce and domestic heating.
Effects: Nitrogen Dioxide is known to reduce the efficiency of breathing and to increase the irritability of airways in the lungs. These effects are reversible.
There is evidence that it increases allergic reactions in the lung, reduces resistance to infection, and that exposure in of children can lead to poorer lung function in later life.
Particulates (PM10)
Sources: Particles in the air come form a range of sources and range widely in size and chemical composition from place to place and time to time.
Natural sources include pollen and sea spray; industrial sources include combustion processes, quarrying and aggregate handling; and transport sources include diesel vehicle exhaust emission, and dust from tyre and brake wear.
Other sources such as smoking produces by far the greatest concentration of particles ingested in those who smoke.
Secondary particulates also occur where other pollutants in the atmosphere combine to form small solid particles.
It is difficult to estimate the relative contribution to the particles in the air for any one place, but transport is considered the biggest source of primary particles, accounting for up to one third of all emissions.
Effects: The effects are likely to vary depending on what the particles in the air actually are, and because it is difficult to do studies on large populations, which can distinguish between different mixtures, the findings tend to be rather generalised.
It is now accepted widely that populations living in areas with higher airborne particle concentrations show a range of differences in health to otherwise similar people. The effects include higher death rates, respiratory and circulatory effects and cancer.
Sulphur dioxide
Sources: Sulphur dioxide is an acidic gas which combines with water vapour in the atmosphere to produce acid rain. Both wet and dry deposition have been implicated in the damage and destruction of vegetation and in the degradation of soils, building materials and watercourses.
SO2 in ambient air can also affect human health, particularly in those suffering from asthma and chronic lung diseases. The principal source of this gas is power stations burning fossil fuels which contain sulphur.
Major SO2 problems now only tend to occur in cities in which coal is still widely used for domestic heating, in industry and in power stations. As many power stations are now located away from urban areas, SO2 emissions may affect air quality in both rural and urban areas.
The last 40 years have seen a decline in coal burning (domestic, industrial and in power generation) As a result, ambient concentrations of this pollutant in the UK have decreased steadily over this period.
Both the Air Quality Strategy and the EU 1st Daughter Directive (1999/30/EEC) contain limit values for ambient concentrations of sulphur dioxide.
Effects: Even moderate concentrations may result in a fall in lung function in asthmatics. Tightness in the chest and coughing occur at high levels, and lung function of asthmatics may be impaired to the extent that medical help is required.
Sulphur dioxide pollution is considered more harmful when particulate and other pollution concentrations are high.